Electrocleaning process



Patented Apr. 25, 1944 ELECTROCLEANING PROCESS Fred F. Martin, Peoria, and John I. Clark, West Peoria, 111., assignors to Caterpillar Tractor Co.,- San Leandro, Calif., a corporation of California No Drawing. Application March. 11,

Serial No. 323,392

'5 Claims. (01. 204-34) Our invention relates to an electrochemical process for cleaning metallic surfaces, and more particularly to the reclamation or salvaging of a metal employed for application of a' protective metallic film on the metal to be cleaned.

A common method employed (in accordance with the teachings of United States patents, Re.

The acid bath where the protective metal film is deposited on the work must be supplied from time to time with an adequate quantity of the desired metal ions to replenish the supply exhausted by the work. A suitable salt of the desired metal may be added to such bath, but it is more economicalto employ the previously mentioned soluble anode of such metal which must be replenished as it is used up. In the case of tin, which is a desirable metal for the purpose because it will alloy with the work whilea metal such as lead will not, replacing the soluble anode thereof is quite expensive, by virtue of the relatively high cost of the metal, which according to the latest quotations runs to about 55 per pound.

From the preceding, it is seen that in the process as heretofore practiced, there has been a loss,

known to the trade as Duriron. Next, the work is subjected to an acid bath, preferably an aqueous solution of sulfuric acid, in which the 'work is made the cathode and in which are employed both substantially insoluble anode electrodes, such as the previously mentioned high silicon iron, and at least one soluble anode electrode of a metal, such as tin, forapplying a protective metal film to the work. Suitable water rinses are generally employed after treatment in .being to shield the work against the acid while the scale is being removed. Frequently, in order to obtain thorough cleansin of the work, it is necessary to subject it to more than one cycle .of treatment. In doing this, the work after treatment in the acid bath and with'the protective metal filmthereornis subjected to the alka-,

line bath. Since the work is the anode in such bath, the protective metal will dissolve from the work which thusbecomes defilmed and it ac cumulates as a heavyspongydeposit on the subdue to the necessity of replenishing the soluble electrode in the acid bath, or supplying a salt of the desired metal in such bath. Our invention is designed to minimize such loss, and has as its objects, among others, the salvaging of the metal employed to deposit a protective film on the work treated in the acid bath, to render more economical a process of the character described. Other objects of our invention will become apparent from a perusal of the following description thereof.

In general, we have found that the substantially insoluble electrodes having the deposit of the protective metal thereon, resulting from treatment of the work in the alkaline degreasing or defilming bath, may be employed as anodes in the acid or descaling bath to replenish the supply of such metal, thus reducing the quantity of soluble anodes of such metal for the 'acid'baththought that the metal content thereof was unstantially insoluble cathode electrodes employed in such alkaline bath. Also, under some circumstanceswhen it is desired to omitthe protective metal film fromthe finally treated work, it must besubjected finally to the alkalinebath where, as was previously explained, theprotective metal film will'dissolve oflf thework and deposit onthe substantially insoluble cathodeelectrodes. Thus,

lt is seen that because the alkaline bath serves at first to degrease the work, and then if subjected again to such bath after treatment in the acid bath, to defllm the work free of the film deposited in the acid bath, it serves both as a dereasing and defllmlng bath.

satisfactory for replenishing the supply inthe adder descaling bath. Such cleaning was a hard, laborious job requiring considerable time.

Thus, itis seen that our process not only salvages the protective metal, but also reduces cost by virtue of elimination of labor heretofore required for cleaning electrodes free of sludge. Instead of emplo'ying'the electrodes with the protective metal-containingsludge, ,as'anodes in the acid or descaling bath, such protective metal containi-ng sludge may be scraped ofi and added to the acid bath at suitable intervals to replenishthe supply of protective metahbut this is not as de sirableas utilizing the electrodes themselves..-

In the preferred procedure of our process, tin is utilized as the protective metal, and we replace some of the substantially insoluble anode electrodes in the 'acid or descaling bath by a corresponding number of the substantially in-' soluble cathode electrodes from the alkaline bath,

and which have the tin containing sludge thereon. The anode electrodes taken from the acid bath are similarly substituted for the cathode electrodes taken from the alkaline bath; and in the alkaline bath they will accumulate the tin containing sludge thereon as defilming of the work proceeds. Whenthe acid bath requires furtheramounts of tin, other electrodes may be I similarly interchanged. Thus, the substantially insoluble electrodes are continuously. rotated among the baths. The electrodes are usually suspended by hooks on heavy conductor bars, and are consequentlyre'adily removable, which enables such interchange or rotation of the substantially insoluble electrodes to be conducted rapidly and with ease.

An electrodehaving the tin containing sludge thereon taken fromthe alkaline bath may be used in the acid bath until it is stripped clean of the sludge, and may be then placed back in the alkaline bath. The operator may readily tell, as he has in the past, when theacid bath requires replacement of the supply of tin so that he may rotate the'elect'rodes in the manner described. In this connection, all the tin used in the process can not be salvaged because frequently, the finished work is provided with a protective tin deposit thereon resulting from final treatment in the acid or descaling bath. Therefore, in our process, it is still necessary to supply iresh soluble tin electrodes in the acid Jan. 1 to June 1 to June 1 Dec. 1 (5 months) (6 months) Total weight in pounds of tin bars used as soluble anode in acid solution 2,080 1,460 Average weight in pounds of replenishing tin used per month 416 243 Average cost per month at average price oi 55c r and $228. 80 $133.65 Average sav gs per month $95. 15

I With respect to the abovedata, substantially the same quantity of material was treated in each of the periods compared.

7 Although we have found our process particularlyadvantageous in salvaging the tin which is preferably employed, the same salvaging operations may be employed with respect to any other metal, such as lead, which may be applied as a protective film to the work in the acid or descaling bath.

I We claim:

1. In the electrochemical process for cleaning metal wherein the metal to be cleaned is the cathode in an electrolytic bath in. which a cleaning treatmentis effected and which deposits a protective metal film thereon, and the anode in another electrolytic .bath in which another cleaning, treatment is efiected and which'removes said protective metal film and deposits the protective .metalon a cathode, the step 01' salvaging said protective metal which comprises utilizing said cathode withsaid protective metal deposit thereon as an anode in said first mentioned bath wherein the protective metal deposit is removed and deposited on the metal to be cleaned.

2. In the electrochemical process for cleaning metal wherein the metal to be cleaned is the cathode in a descaling electrolytic bath containing a substantially. insoluble anode and a soluble anode of ametal which is deposited as a protective film on said metal to be cleaned, and said metal to be cleaned is the-anode in another electrolytic bath which defilms said protective metal film from'the metal to be cleaned and deposits the protective metal on a substantially insoluble cathode, the step of salvaging said protective metal which comprises substituting said substantially insoluble cathode with said protective metal deposit thereon for said substantially insoluble anode in said descaling bath whereby said protective metal deposit will be removed in said descaling bath and the metal thereof deposited on said metal to be cleaned; g

3.1In the electrochemical process for cleaning metal wherein the metal to be cleaned is the cathode in a descaling electrolytic bath containing a plurality of substantially insoluble anode electrodes and a soluble anode of a metal which is depositedas a protective film on said metal to be cleaned, and said metal to be cleaned is the anode in another electrolytic bath which defilms said protective metal film from the metal to be cleaned and deposits the protective metal on a plurality of substantially insoluble cathode electrodes, the step of salvaging said protective metal 'which comprises rotating said substantially insoluble electrodes by exchanging cathode electrodes with said protective metal deposit thereon for anode electrodes in said descaling bath.

4. In the electrochemical process for cleaning metal wherein the metal to be cleaned is the cathode in an acid electrolytic bath containing a plurality of substantially insoluble anode electrodes and a soluble anode of tin which is deposited as a protective film on said metal to be cleaned, and said metal to be cleaned is the anode in an alkaline electrolytic bath which removes said tin film from said metal to be cleaned and deposits the tin on a plurality of substantially insoluble cathode electrodes, the step of salvaging said tin which comprises replacing substantially insoluble anode, electrodes in the acid bath by cathode electrodes in the alkaline bath containing tin deposit thereon. v

5. In the electrochemical process for cleaning metal wherein the metal to be cleaned is a cathode in an acid electrolytic bath containing,

a substantially insoluble anode electrode and a soluble anode of a metal which is deposited as a protective film on the metal to be. cleaned,

JOHN I.' CLARK.

FRED F. 

